1. Field of the Invention
The present invention relates to a dial for a timepiece, a manufacturing method thereof and a timepiece.
2. Description of the Related Art
According to an earlier development, there is a dial for a timepiece, such as a wristwatch, comprising a luminescent member made of an EL element (Electro Luminescent element) for emitting light to enable users to recognize time even in a dark place.
As this type of a dial for a timepiece, for example, there is one that comprises a decoration member having a plurality of through holes on a luminescent member so that the luminescent member emits light upwards through each of the through holes for illuminating the upper surface of the decoration member. There are U.S. Pat. Nos. 5,838,640, 5,930,204, 5,880,796 and 6,020,943 and U.S. patent application Ser. No. 09/323,449 (now U.S. Pat. No. 6,266,297), Ser. No. 09/152,410 (now U.S. Pat. No. 6,208,591) and Ser. No. 09/702,259, as earlier developments of the present invention.
One problem encountered in such a dial is the through holes. If the diameter of the through holes is small, the light from the luminescent member cannot pass through them enough to illuminate the dial, so that the dial becomes dark. On the other hand, the through holes with a large diameter become so visible that the appearance of the dial leads sense of incongruity.
The object of the present invention is to emit light from the luminescent member upwards effectively and to make the through holes discreet enough to improve a good showing.
The present invention was developed to solve the above-described problem. According to a first aspect of the present invention, a dial (20, 29) comprises a decoration member (21) that has a plurality of through holes (22) formed vertically and is provided on an upper surface of a luminescent member (10). Moreover, the through holes are formed so that the cross-sectional area of holes (24, 27, 28) that is a lower surface side portion of the through holes is larger than the cross-sectional area of holes (23) that is an upper surface side portion of the through holes.
According to the invention, the cross-sectional area of the lower-side holes of the through holes is larger than the cross-sectional area of the upper-side holes. Therefore, the upper-side holes can be formed to be so small that the through holes are discreet from above, when the decoration member is used for a dial. As a result, the dial can have a good showing. Furthermore, it is possible to sufficiently take in light from the luminescent member through the lower-side holes. Therefore, even if the diameter of the upper-side holes is small, the enough amount of light can pass through the through holes to obtain the sufficient intensity of illumination. As a result, the upper portion of the decoration member can be illuminated brightly.
A second aspect of the invention is a manufacturing method of a dial for a timepiece comprising two processes, as shown in FIGS. 3A-3D and 9A-9D. According to the first process, masks (25, 26, 35, 36) are provided to cover both upper and lower surfaces of a substrate 15. The masks have openings (25a, 35a) on the upper surface and openings (26a, 36a) on the lower surface so that the upper-side openings (25a, 35a) corresponds to the lower-side openings (26a, 36a). Moreover, the upper-side openings (25a, 35a) are smaller than the lower-side openings (26a, 36a). Therefore, a plurality of through holes are formed on the substrate by etching from both surfaces to provide a decoration member (21, 31, 41). According to the second process, the decoration member is mounted on an upper surface of a luminescent member (10).
According to the invention, a substrate is provided with masks having openings on both surfaces, wherein the upper-side openings are formed at the positions corresponding to the lower-side openings. Thus, through holes are formed at positions corresponding to the openings by etching from both surfaces. Therefore, even if a substrate is thick, it is possible to provide smaller through holes than that provided by etching from only one side. As a result, the through holes can be formed to be discreet.